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Technical Can you adjust mechanical fuel pump pressure?

Discussion in 'The Hokey Ass Message Board' started by NAES, Jul 17, 2019.

  1. NAES
    Joined: Dec 24, 2008
    Posts: 479

    NAES
    Member

    I just installed a new AC Delco fuel pump on my '53 Chrysler with a Mopar 360 topped with an Edelbrock 4barrel (1806) carb in there. There was fuel pooling at the top of the pump seam. It ran like hell afterwards and initially blamed the carb. But starting from the tank and moving up I replaced fuel lines and filters. Then measured fuel pressure and I'm getting 7.5 psi which is a little high according to Edelbrock.

    I see these god awful looking adjustable fuel pressure regulators available but was hoping an old timer might know a trick or 2 to dial down the pressure at the pump. Maybe bending the arm a bit or shimming it out, etc?

    Thanks for any advice guys. NAES

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  2. squirrel
    Joined: Sep 23, 2004
    Posts: 46,864

    squirrel
    Member

    The pressure is determined by the spring inside the pump, which is kind of hard to change on a pump that's crimped together.

    If the pump is leaking, I suggest you first look carefully for leaks at the fittings, or oil or coolant dripping onto the pump from elsewhere. If it's really leaking fuel from the seam, take it back and get a new pump.
     
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  3. NAES
    Joined: Dec 24, 2008
    Posts: 479

    NAES
    Member

    Sorry Squirrel, the old pump was leaking after 10 years of use, not the new one.

    Ok, so a pressure regulator is needed. Are there any overly simple looking units in existence with just a couple of fittings and some type of needle seat to regulate pressure? What I'm finding are these gaudy chromed out units that are more suited for high performance engines. I would prefer something that kinda blends into the engine bay. If that makes sense.

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  4. NAES
    Joined: Dec 24, 2008
    Posts: 479

    NAES
    Member

    Since there's gonna be a little downtime and I have a carb spacer on order to keep heat away from the carb I figured it was time to peek inside. Yikes is all I can say! Even with filters being changed somewhat regularly over the past 10 years, a ton of garbage was still floating around in there!

    Wifey decided it was time for a photo-op.

    NAES 20190717_192856.jpeg

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  5. alchemy
    Joined: Sep 27, 2002
    Posts: 15,868

    alchemy
    Member

    There are many threads explaining peoples' problems with the round dial type regulators. Most everyone (myself included) has had good luck with the Holley regulators. They come in at least a couple different ranges, so make sure to pick the one that your carb wants to live with. Also install a gauge in the system so you know exactly what you are dialing in.
     
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  6. Your Edelbrock will be happy with 4 1/2- 6 psi max- also while you have it apart make sure the floats are set to Edelbrock spec and you should be good to go


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  7. Does the pump have a return line that you plugged off?
    Are you reading 7.5 running or deadheaded?
     
  8. NAES
    Joined: Dec 24, 2008
    Posts: 479

    NAES
    Member

    Good question Mark!

    I just stabbed the gauge into the end of the fuel line and cranked to get my reading. The engine was not running at the time.

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  9. Seems like it woulda started if it had gas in the carb. Anyway, not a good test. What about a return port?
     
  10. NAES
    Joined: Dec 24, 2008
    Posts: 479

    NAES
    Member

    Yes the engine ran with the new pump but it didn't run well at all which is why I went through the fuel system prior to pulling the carb to dive inside.

    I do not have a return line currently. I have a line from the tank to the pump then a hard line from the pump directly to the carb. I have never heard of using a return line with a mechanical pump but I also am not a fuel system expert by any means. So if I can run some type of inline check valve with a return dumping back "behind" the pump to belld off the extra few pounds of pressure, that sounds like a great option.

    What would I look up for this check valve setup?

    Thanks everyone for the help. NAES

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  11. NAES
    Joined: Dec 24, 2008
    Posts: 479

    NAES
    Member

    This is the gauge I used to measure the fuel pressure. Do I need to modify it with a "T" fitting so the fuel is passing through the entire unit with the engine running to get an accurate reading?

    And an impromptu wifey pic to show I'm tryin' here guys! Lol 1563422782286.jpeg IMG-20190717-WA0000.jpeg

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  12. squirrel
    Joined: Sep 23, 2004
    Posts: 46,864

    squirrel
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    it would be a good idea to measure fuel pressure with the engine running.

    Return lines were used for a long time, usually on cars with big engines that would get pretty warm, and tend to vapor lock. Usually they had three fittings on the pump, the return was an added 1/4" hose fitting. Another way to run a return line is to us a filter such as a Wix 33040 or 33041 (for 5/16 or 3/8 line respectively) that has a fitting for a return line. But that won't really regulate pressure.

    I run 6 or 7 psi with Carter AFBs on my go fast cars, using an electric pump and pressure regulator, they seem to do fine like that. The regulator is the Holley that's kind of large, and can be adjusted precisely.
     
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  13. carbking
    Joined: Dec 20, 2008
    Posts: 2,871

    carbking
    Member

    An original pump from 1953 should be rebuildable (held together with screws). As Jim stated, the pressure that the pump can produce is dependent on the tension of the diaphragm spring. I know different tension springs were used in different pumps. I do not know if individual springs are available ala carte.

    Then & Now Automotive, in the Boston area, is an excellent source of fuel pump kits.

    The first return lines of which I am aware, were used on late 1950's vehicles with A.C., and as Jim mentioned, were an extra tap on the fuel pump.

    We started suggesting the inline 3-line filter at the carburetor maybe 40 years ago. With the garbage fuel, the inline is more beneficial than the tap at the pump, as it protects more of the fuel line.

    Jon.
     
    Last edited: Jul 18, 2019
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  14. NAES
    Joined: Dec 24, 2008
    Posts: 479

    NAES
    Member

    The engine has been swapped to a 70's era 360 so no fuel pump rebuilding going on here.

    Thanks for the pressure regulating ideas.

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  15. RookieFixItMan
    Joined: Mar 24, 2020
    Posts: 1

    RookieFixItMan

    Inspired by ideas here, I rigged up a return line on a Ford 300, YF 1 BBL carb. Mechanical pump was knocking out 6-8 PSI. Variable flow on return line knocked it down 3-5 psi, with good control.
     

    Attached Files:

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  16. Halfdozen
    Joined: Mar 8, 2008
    Posts: 606

    Halfdozen
    ALLIANCE MEMBER

    Malpassi regulator. Made in Italy, all aluminum, no chrome plated plastic. Comes with brass hose barbs, body has female NPT threads, different styles. Good quality.
     
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  17. clem
    Joined: Dec 20, 2006
    Posts: 2,996

    clem
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  18. mkubacak
    Joined: Jun 20, 2005
    Posts: 167

    mkubacak
    Member

    I wonder what, if anything ever solved @NAES problem?
     
  19. NAES
    Joined: Dec 24, 2008
    Posts: 479

    NAES
    Member

    I added a 1" phenolic carb spacer along with running Thermacool from evaporust for about a week. That combo has seemed to do wonders for my problems but I haven't driven in hot weathervyet to really test the system.

    As of now I'm optomistic.

    NAES

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  20. ClarkH
    Joined: Jul 21, 2010
    Posts: 949

    ClarkH
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    You can get a new Malapassi regulator that looks like it belongs there. There's also a version with built-in filter. Pressure is adjusted via a screw under the acorn nut (see picture). Filter King model comes with a removable pressure gauge to help you set it.

    "Petrol King" Model (regulator only):
    Malapassi-Petrol-King.jpg

    "Filter King" Model (regulator and filter + comes with gauge):
    Malapassi-Filter-King.jpg
    You can also get the Filter King with a glass bowl, if you prefer.
     
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  21. sliceddeuce
    Joined: Aug 15, 2017
    Posts: 2,982

    sliceddeuce
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    Yes...A glass bowl would be traditional.:rolleyes:
     
  22. BJR
    Joined: Mar 11, 2005
    Posts: 6,518

    BJR
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    Wouldn't a spacer between the pump and block reduce the stroke and the pressure? My 52 Willys jeep has a spacer between the pump and block. Or does this just reduce the volume? Squirrel?
     
  23. Mimilan
    Joined: Jun 13, 2019
    Posts: 641

    Mimilan
    Member

    You can do a pressure regulator that is "almost" invisible.

    "T" off a return line after the pump [back to the tank]
    This T can be down by the pump or up by the carb , it doesn't matter as all pressure is equalized.

    Anywhere in the return line fit a pressure adjustable "Check Valve" [these can be adjusted with different springs]
    Any pressure above the seat pressure just dumps back in the tank.

    Chevy 6.5 Diesels have them on the return line to control lift pump pressure [3-5psi]

    This was a common method in NZ V8 touring cars to prevent vapour lock, and electric gerotor pump failure

    Fuel-Pressure-RegulatorCheck-Valve.jpg
     
  24. Mimilan
    Joined: Jun 13, 2019
    Posts: 641

    Mimilan
    Member

    Unfortunately the almighty squirrel is mistaken.[ This is his first mistake ....ever :D ]

    Fuel pressure in a diaphragm pump is controlled by the Inlet and Outlet valves "Seat pressure"
    They need to close properly to maintain a one-way flow.
    If the fuel pressure exceeds the seat pressure the valves stay open and the fuel just oscillates with the diaphragm pulses

    [ it's similar to doing a compression check with valves stuck open]

    fuel pump.jpg
     
  25. denis4x4
    Joined: Apr 23, 2005
    Posts: 3,552

    denis4x4
    ALLIANCE MEMBER
    from Colorado

    Amazon’s price for the glass bowl regulator is $140!
     
  26. Budget36
    Joined: Nov 29, 2014
    Posts: 4,245

    Budget36
    Member

    When I had the last FH V8 and electric pump, I was flooding the carb. Here on the HAMB I was directed to guys that used to work for Holley and started their own business, I got a regulator from them at less than Holley price and the universe under the hood was excellent:)

    Damned if I can recall them tho.
     
  27. ClarkH
    Joined: Jul 21, 2010
    Posts: 949

    ClarkH
    ALLIANCE MEMBER

    If you mean the Malapassi, try eBay. Way less.
     
  28. clem
    Joined: Dec 20, 2006
    Posts: 2,996

    clem
    Member

    Yep, I paid NZ$230 approx with the alloy version, pricey, but after having nothing but trouble with several other, this was to be my last attempt to get it right.
    Wanted the glass version but the guy said that over around 10lb pressure, the glass bowl tended to leak. - (the 7 lb pump I bought puts out 9lb).
     
  29. Boden
    Joined: Oct 10, 2018
    Posts: 722

    Boden

    I like the offy adjustable inline one


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  30. carbking
    Joined: Dec 20, 2008
    Posts: 2,871

    carbking
    Member

    Without going into brands (I haven't looked at every fuel regulator on the face of the planet); I have seen two basic types of regulators:

    (1) one with a bypass
    (2) one without a bypass

    The one with the bypass has a valve (often adjustable to a specific pressure) that will open if that pressure is exceeded, shunting fuel, thus pressure, either back to the tank, or more commonly, back to the inlet side of the regulator.

    The one without a bypass (the inline dial-types generally) regulate pressure by regulating volume. The regulator will simply clamp down on the orifice passing the fuel from inlet to outlet. At the rated flow (often 15 gal/hr or 20 gal/hr) the output pressure will be close to the value dialed. At low flow (i.e. idle conditions) the outlet pressure and the inlet pressure are often the same, regardless of the dial value.

    Jon.
     
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